This invention relates to an apparatus for performing fermentation treatment of organic waste containing water content such as garbage or the like to make organic fertilizer or the like. Particularly, it relates to an apparatus for performing fermentation treatment which allows the conditions of fermentation treatment such as temperature of the waste or percentage of water content of the waste to be maintained most suitably, so that fermentation treatment can be performed in a short time and efficiently.
Various kind of treatment machines for performing fermentation treatment of organic waste to make fertilizer for recycling are developed and. used, said organic waste, for example, including garbage which arises from homes, restaurants, super markets or the like, excrete and garbage which arises from fishery markets, fruit and vegetable markets, poultry farming places or pig farming places, or garbage which arises from food processing industry.
Such fermentation treatment apparatus of waste is disclosed in, for example, Patent Laid-open Gazette Hei-7-68239, Patent Laid-open Gazette Hei-9-47747, Patent Laid-open Gazette Hei-9-77581, and Patent Laid-open Gazette Hei-9-165283. These disclosed apparatuses use hot water or electric heaters as heating means for making temperature and percentage of water content suitable for fermentation treatment of waste. Further, in order to ascertain that humidity within the fermentation tank is a value suitable for fermentation treatment, a humidity sensor is attached within the fermentation tank to control the humidity within the fermentation tank.
Since these fermentation treatment apparatuses in the prior art use hot water or electric heaters as heating means, there is a disadvantage in that it is impossible to heat the whole waste suitably and to treat it efficiently with fermentation, particularly, in the case where a large quantity of waste is treated, there is a disadvantage in that it is difficult to maintain said waste within a range of temperature suitable for fermentation, so a long time is required to perform good fermentation. That is to say, even when the waste is heated using hot water or an electric heater in a circulating way or in a continuous way, in the case of hot water, although such hot water itself can be used within a range of temperature suitable for fermentation or at a temperature near thereto, with hot water at such a temperature, it is difficult to give a large quantity of heat to said waste in order to make the waste to a temperature suitable for fermentation. Furthermore, in the case of electric heaters, the waste is heated to a temperature rather higher than a temperature in a range suitable for fermentation, so irregularity of heating is caused and good fermentation cannot be performed.
Moreover, it is necessary for efficient fermentation treatment to change and regulate the driving conditions according to variation of the quantity and composition of the waste as the occasion demands, however, in the conventional fermentation treatment apparatus, it is difficult to control promptly and accurately the humidity within the fermentation tank which is one of the above-described driving conditions. For example, in the apparatus disclosed in Patent Laid-open Gazette Hei-9-77581, after the state of humidity within the fermentation tank is detected, i.e., after a change in the humidity within the fermentation tank is detected, feedback is performed and ON-OFF operation of a ventilation fan is made to exhaust the air within the fermentation tank or to supply fresh air into the fermentation tank. As a result, a time lag occurs to change the humidity within the fermentation tank to a predetermined value, so, the state of humidity cannot be maintained accurately.
The present invention aims at maintaining the conditions of fermentation treatment such as temperature and humidity of the waste most suitably, so that fermentation treatment of waste can be performed quickly and efficiently.
A fermentation treatment apparatus of organic waste according to the present invention, which comprises a fermentation tank for housing organic waste, and a means for maintaining the waste within said fermentation tank in the conditions suitable for fermentation treatment, characterized in that as one of said maintaining means, gas which performs gas-liquid change within a range of temperature suitable for fermentation, particularly steam vapor reduced in pressure is used, whereby the waste is heated and maintained in such heated condition due to a change of said gas. It is widely known that a relation between pressure and temperature in steam pressure is determined clearly (saturated steam pressure curve). For example, in the case of steam vapor, it amounts to 100xc2x0 C. at 760 mm Hg, approximately 80xc2x0 C. at 360 mm Hg and approximately 40xc2x0 C. at 60 mm Hg. Further, in the case of ethanol steam, approximately 80xc2x0 C. at 760 mm Hg, and; approximately 40xc2x0 C. at 130 mm Hg. In this way, pressure is changed to make die temperature of said gas to that within a range of temperature suitable for fermentation of said gas and large condensation heat generated at the time of vaporization of said gas is used for beating waste.
Steam vapor at reduced pressure can be supplied by reducing the steam at a relatively high pressure, for example, a steam pressure at 5 kg/cm2 or 3 kg/cm2 generated by a normal boiler or the like, to atmospheric pressure or so, or to a pressure lower than atmospheric pressure by way of a pressure regulating valve or a reducing valve or the like. Furthermore, by keeping the interior of the primary side heat treatment device or the interior of the jacket part at a state of a predetermined reduced pressure, or by connecting the interior of the primary side heat treatment device or the interior of the jacket part to a suction means such as a vacuum pump to keep a predetermined state of reduced pressure, the waste can be treated with heat using a desired reduced pressure steam, i.e., the steam at a temperature suitable for fermentation lower than 100xc2x0 C. there are two cases, one being the case of treatment being performed in the air and the other being the case of treatment being performed in the ambient atmosphere of predetermined gas which is exhausted of air. Depending on the kind of fermentation bacteria used at the time of fermentation treatment, if the fermentation bacteria is aerobic, fermentation treatment is performed in the air ambient atmosphere, and if it is anaerobic, fermentation treatment is performed in the predetermined gas ambient atmosphere which is exhausted of air.
Preferably, said fermentation tank is provided at the primary side thereof with a heat treatment device, and use of steam vapor lower than an atmospheric pressure is possible as a heat source for maintaining said heat treatment device in a temperature suitable for heat treatment. In the case where fermentation treatment of organic waste such as excreta of domestic animals is performed, arranging the heat treatment device at the primary side of the fermentation tank and using the steam vapor at a reduced pressure as a heat source allows a process of fermentation treatment to be performed efficiently and in a short time, by heating the waste to a suitable temperature with a large quantity of heat generated at the time of liquefaction to adjust previously the percentage of water content of the waste to a value in a range suitable for fermentation treatment, or by performing preliminary fermentation to recover methane gas.
Preferably, an absorbing means is connected to a heat exchange part in which heat exchange is performed between said gas and waste.
Moreover, in an fermentation treatment apparatus comprising a fermentation tank for housing organic waste, and a means for maintaining the waste within said fermentation tank in a state suitable for fermentation treatment, as one of said maintaining means, a means for regulating the humidity of the air supplied to the waste to a value suitable for fermentation treatment is provided, whereby said regulating means is adapted to regulate the humidity of the air which flows through an air supply part provided for supply of air into the above-described fermentation tank. Also in such a case, the conditions of fermentation treatment can be improved and the action of fermentation bacteria is activated so that fermentation treatment of the waste can be performed promptly and efficiently.
Preferably, the above-described regulating means is a humidification fluid injecting means, and a humidity detecting means is attached to the fermentation tank side of said humidification fluid injecting means, to thereby control a quantity of injection of fluid from the humidification fluid injecting means depending on the detected value of said humidity detecting means.
Provision of the humidification fluid injecting means at the air supply part allows the humidification fluid, for example, steam or spray water or the like to be injected into the air supplied into the fermentation tank to thereby cause a change in the humidity of the air. Furthermore, attaching a temperature detecting means to the fermentation tank side of the humidification fluid injecting means allows the humidity of the air supplied to the fermentation tank to be detected and allows a quantity of injection of fluid from the humidification fluid injecting means to be controlled, so that the humidity of the air supplied to the fermentation tank can be maintained to a predetermined value. Since the humidity of air supplied to the fermentation tank can be made to a predetermined value previously, the humidity within the fermentation tank can be controlled precisely in a state suitable for performing fermentation treatment.
After the air before injection of steam or water is heated to, for example, 100xc2x0 C. or so, steam or water is injected, and thereafter, heat exchange of said air is performed to thereby cool it to, for example, 60xc2x0 C., whereby the humidity and, further, temperature of said supplied air can be controlled more precisely.
With regard to control of a quantity of injection of humidification fluid, the humidification fluid injecting means is provided with a valve means, which allows the opening degree thereof to be adjusted, and a quantity of injection of steam or a quantity of water can be controlled by adjustment of the opening degree of the valve means. Moreover, a plurality of spray nozzles are attached to the humidification fluid injecting means, and the above-described control may be performed by adjusting the opening degree of the nozzle or the number of the opened nozzles.
More preferably, the above-described air supply part is provided with a oxygen enrichment means. Such oxygen enrichment means makes the concentration of oxygen in the supplied air most suitable for fermentation bacteria to thereby realize efficient fermentation. The oxygen enrichment means may be constituted in such a way as to adsorb nitrogen in the air using zeolite as a adsorbing means, or may be provided with a oxygen enrichment membrane as a gas separating membrane, or a membrane of liquid crystal or the like utilizing selective permeation function may be used.